Field of the Invention
The present invention relates to a wide angle optical system, and particularly to an optical system which enables to observe simultaneously an object in front and an object on a side.
Description of the Related Art
An optical system that enables to observe simultaneously an object in front and an object on a side has been disclosed in Japanese Patent Application Laid-open Publication No. 2008-309861 and Japanese Patent Application Laid-open Publication No. 2011-48086.
The optical system disclosed in Japanese Patent Application Laid-open Publication No. 2008-309861 includes in order from an object side, a front group having a negative refractive power, an aperture stop, and a rear group having a positive refractive power. The front group includes a first lens group having a negative refractive power and a second lens group. The rear group includes a third lens group having a positive refractive power and a fourth lens group having a positive refractive power. The first lens group includes a negative lens or one of a negative lens and a positive lens.
The optical system disclosed in Japanese Patent Application Laid-open Publication No. 2008-309861 has a direct-viewing optical path and a side-viewing optical path. In the direct-viewing optical path, a third transmitting surface and a fourth transmitting surface are disposed. In the side-viewing optical path, a first transmitting surface, a first reflecting surface, a second reflecting surface, and a second transmitting surface are disposed.
The optical system disclosed in Japanese Patent application Laid-open Publication No. 2011-48086 includes in order from an object side a front group and a rear group. The front group includes a first lens group having a negative refractive power and a second lens group. The rear group includes a third lens group having a positive refractive power. The first lens group includes a negative lens.
The optical system disclosed in Japanese Patent Application Laid-open Publication No. 2011-48086 includes a first optical system and a second optical system. The first optical system is for observing an object in front, and includes the first lens group, the second lens group, an aperture stop, and the third lens group. The second optical system is for observing an object on a side and includes the second lens group, the aperture stop, and the third lens group.
In the first optical system, light from the object in front passes through the first transmitting surface and the second transmitting surface. In the second optical system, light from the object on a side passes through a third surface, a second reflecting surface, a first reflecting surface, and a second transmitting surface.